Thyroid function in the elderly has been a matter of discussion. The universe of the present study includes males and females 36 hospitalized with an average age of 72.97 +/- 8.70 years (group I) and 36 ambulatory asymptomatic elderly with 69.81 +/- 8.55 years of age (group II). Serum levels of T3, T4, T4L and TSH were measured in both groups. Mean values of T3 were significantly lower in the hospitalized patients than in the control group. The difference persisted on both, males and females, analyzed separately. Mean values of T4L were significantly lower in women of group II, while mean values of T3 were significantly lower in men of group I. The comparison of thyroid function tests in male and female showed that serum values of T3 and T4 were significantly lower in men of group I. By dividing results in age categories, serum levels of T4L in group II were significantly lower in the age group of 70 to 79 and 80 to 89. Thyroid function tests in asymptomatic ambulatory elderly tend to be normal, whereas the hospitalized patients showed a high proportion of alterations.